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The present invention relates generally to an optical position alignment sensor for aligning electronic components, which sensor is used in the electronic component placement industry. Machines of the type used in the electronic component placement industry are sometimes called pick and place machines.
Electronic shadowing techniques incorporated in optical-based sensors are in widespread use today in pick and place machines for mounting electronic components on printed circuit boards. One of the more commonly used position alignment sensors is manufactured by CyberOptics Corporation in Golden Valley, Minn. and is sold as a LaserAlign(copyright) component alignment sensor. This sensor uses a light source focused into a stripe of light, which is typically incident on the side of an electronic component, thereby forming a shadow which is cast onto a detector. When the electronic component is rotated (by a nozzle controlled in x, y and z direction by the pick and place machine), the shadow cast on the detector changes in width.
The orientation process is generally carried out while the pick and place machine is transporting the component to a target printed circuit for placement. When the orientation process is carried out simultaneously with the transport of the component, the orientation process is sometimes referred to as an xe2x80x9con-headxe2x80x9d or an xe2x80x9con-the-flyxe2x80x9d measurement. Conversely, xe2x80x9coff-headxe2x80x9d measurements are made when the sensor is not affixed to the pick and place head but rather, is stationary relative to the head.
Current techniques are susceptible to error caused by glint. This occurs where illumination falling on a portion of the component is reflected onto the detector. This condition can lead to erroneous data and improper detection. One of the problems typically not addressed by the prior art is a position alignment sensor for aligning at least two components which prevents undesirable glints (i.e., reflections), both large and small angle, from interfering with accurately orienting either of the components.
A method of controlling glint in a position alignment sensor which aligns a component is provided. The method includes providing a stripe of light directed toward the components. The components block the light to cast shadows of the outline of the components. Some of the light is specularly reflected from the component to provide a glint. The light is then passed through a filter. The filter rejects the glint. The rejection of the filter is tuned by rotating the filter about an axis in the plane of the component. A detector is positioned beyond the filter to detect the shadows. Such a filter can be realized with a dielectric coating.
Another aspect of the invention is a position alignment sensor adapted to align components. The sensor includes a housing that accepts at least one component. A light source is located in a source plane for shining light on the component. Furthermore, the light is oriented substantially perpendicular to a central axis of each of the components so that the components block the light to form a shadow image. A glint specularly reflects off the component. A filter receives the light and allows the light to pass while rejecting the glint. The filter is tunable by rotating it about an axis in the plane of the component. A detector is positioned behind the filter.
In another aspect of the invention, two types of undesireable glints (small and large angle glints) are effectively filtered in an optical position alignment sensor and method designed to orient at least two components. The method includes shining a plurality of rays of light onto the components, the rays directed generally perpendicularly to a central axis of each of the components where each of the components clock the rays to cast a shadow of the outline of the components. Some of the rays of light are specularly reflected from one of the components to provide a large-angle glint, which is the first type of flint reduces by the present invention. The method then passes the rays of light through an optic with positive power so as to focus the two shadows at a focal point, the optic focuses an image of the shadows at a component plane located behind the focal point. An aperture is positioned substantially at the focal point and an opening in the aperture is positioned to allow the rays of light to pass therethrough except for the large-angle glint. The combination of the positive optic and the aperture prevents the large angle glint from reaching the detector. A detector is positioned in front of the component plane and a plane of the detector is positioned parallel to the plane of the optics, so that an unfocused image of the shadow falls on the detector. Additional software to differentiate between areas of differing intensities and the shapes of such areas, is needed to discern the glint from the shadow. The placement of the detector in front of the component plane separates the component shadow edge from the glint signature to suppress the effect of the small angle glint of the present invention.